1. Field of the Invention
The present invention relates to an air tool such as an air grinder or the like with a safety device.
2. Description of the Related Art
Conventionally, an air grinder driving an abrasive member prevents over-speed by reducing the amount air consumption at low load and by increasing the amount of air at heavy load. Such control maintains a roughly constant speed at all values of load. For these purposes, an air grinder generally includes a speed adjusting apparatus capable of controlling the rotational speed at high and low load.
Referring now to FIGS. 4, 5a and 5b, a speed adjusting apparatus 30 in a main body casing 28 of a prior art air grinder includes a rotary member 31 having a flange portion near the center on a side surface of a cylinder. A speed adjusting valve body 36 includes a flange portion near the bottom of the side surface of the cylinder. A speed adjusting weight 32, having a substantially L-shaped cross section as seen from the side is pivoted below rotary member 31.
A valve seat 38 is interposed in an air passage 29 within the main body casing 28. An air motor 40 is driven by air supplied through the air passage 29. The rotary member 31 is directly connected to an output shaft 41 of the air motor 40. Rotation of the air motor 40 is directly transferred to the rotary member 31. The speed adjusting valve body 36 is fitted to the outside of the rotary member 31. The speed adjusting valve body 36 is free to slide in an axial direction along the outer surface of the rotary member 31. The speed adjusting valve body 36 and the valve seat 38 of the air passage 29 are positioned facing each other.
Spring receivers 39, 39 protrude diametrically outward on both opposing side surfaces above the rotary member 31. The respective spring receivers 39 and 39 are fitted into axially elongated holes pierced through opposing side surfaces of the rotary member 31 above the speed adjusting valve body 36. A speed adjusting valve spring 37 is interposed between the spring receivers 39, 39 and the flange portion of the speed adjusting valve body 36. The speed adjusting valve body 36 is urged by the speed adjusting valve spring 37 in a direction away from the valve seat 38.
The speed adjusting weights 32 and 32, having an a substantially L-shaped cross section as seen from a side view, are each pivoted on a pin 34. The speed adjusting weights 32, 32 each includes a weight portion 33 and a lever portion 35. As the rotational speed of rotary member 31 increases, the weight portions of the speed adjusting weights 32, 32 are urged outward by centrifugal force about their pins 34, 34. This tilts the speed adjusting weights 32, 32, as shown in FIG. 5a so that the lever portions 35, 35 apply an upward force on the flange portion of the rotary member 31.
In operation, at light load, the speed adjusting apparatus 30 assumes the configuration shown in FIG. 5a. Centrifugal force on the weight portions 33, 33 of the speed adjusting weight 32, 32 due to the rotation of the air motor 40, tilts the weight portions 33, 33 outward around their respective pins 34, 34. The lever portions 35, 35, in contact with the flange portion of the speed adjusting valve body 36, apply a force in an upward direction for urging the speed adjusting valve body 36. This moves speed adjusting valve body closer to the valve seat 38. When the thrust applied by the speed adjusting weights 32, 32 exceeds the opposing force of the speed adjusting valve spring 37, the speed adjusting valve body 36 is displaced upward, thereby decreasing the effective opening of the air passage through the valve seat 38. As a result, the amount of air supplied through the air passage 29 is reduced, and the rotational speed is correspondingly reduced.
Referring now to FIG. 5b, under heavy load on an abrasive member, such as a grindstone or the like (not shown), the rotational speed of the air motor 40 is reduced. As a result, the centrifugal force applied to the speed adjusting weight 32 is reduced. Accordingly, the thrust applied in the upward direction to speed adjusting valve body 36 is also reduced. Accordingly, the speed adjusting valve body 36 is pressed downward by the speed adjusting valve spring 37 to move the speed adjusting valve body away from the valve seat 38. This increases the effective opening of the air passage thereof As a result, an amount of air supplied from the air passage 29 is increased, and the torque output of the air motor 40 is increased. As a result, slowing of the air motor 40 under heavy load is reduced. As mentioned above, the rotational speed of the air motor is automatically adjusted by the speed adjusting apparatus 30.
However, if the speed adjusting apparatus 30 mentioned above does not operate normally for some reason, for example, because of foreign material in the speed adjusting apparatus 30, a dangerous over-speed condition may result. In the conventional device, the only way to prevent this danger is to perform periodic inspections by dismantling the device.
It is an object of the present invention to provide an air tool which overcomes the conventional disadvantages mentioned above.
It is a further object of the invention to provide an air tool having a safety device which automatically reduces the rotational rate and locks the air tool to inhibit normal use when rotation generated by an air motor of the air tool exceeds a predetermined rotational speed.
Then, in accordance with a first aspect of the present invention, there is provided an air tool with a safety device comprising: a main body casing 22, an air passage 23 formed within the main body casing 22, an air motor 26 rotated by air supplied from the air passage 23, a valve seat 24 interposed in the air passage 23, a safety valve body 4 arranged in such a manner as to change an effective opening of the passage by moving in a direction of moving close to and apart from the valve seat 24, first urging means 6 for urging the safety valve body 4 in a direction of moving close to the valve seat 24, a rotary member 2 rotating in interlocking with an output shaft 25 of the air motor 26, a safety valve stopper 16 mounted to the rotary member 2 so as to be displaced outward in a diametrical direction due to a centrifugal force generated by a rotation of the rotary member 2, and second urging means 20 for urging the safety valve stopper 16 in a direction inverse to a direction in which the centrifugal force is applied, wherein a lock mechanism for locking a motion of the safety valve body 4 in a steady operation state that the safety valve body 4 moves apart from the valve seat 24 against an urging force of the first urging means 6 so as to increase an effective opening of the passage, disengaging the lock so as to move the safety valve body 4 in a direction of moving close to the valve seat 24 by the first urging means 6, thereby reducing the effective opening of the passage when a rotation rate of the output shaft 25 of the air motor 26 is increased to be over a predetermined rotation rate and the safety valve stopper 16 moves against the urging force of the second urging means 20 due to the centrifugal force, and again locking the motion of the safety valve body 4 in this state is provided between the safety valve body 4 and the safety valve stopper 16.
In accordance with the air tool with the safety device described in the first aspect mentioned above, when the rotational speed of the output shaft 25 of the air motor 26 exceeds a predetermined speed of rotation, for example, 10 to 15% of a normal rotational speed, the safety valve stopper 16 locking the motion of the safety valve body 4 mentioned above moves against the urging force of the second urging means 20 due to the centrifugal force so as to disengage the lock, and the safety valve body 4 mentioned above moves close to the valve seat 24 due to the urging force of the first urging means 6 so as to reduce the effective opening of the passage of the valve seat 24 mentioned above, thereby limiting the amount of air supplied from the air passage 23. To maintain the locked condition mentioned above, the safety valve stopper 16 again locks the motion of the safety valve body 4.
In accordance with a second aspect of the present invention, there is provided an air tool with a safety device, further comprising air supply means for supplying a small amount of air from the air passage 23 the safety valve body 4 during the locked condition.
In accordance with the air tool with the safety device described in the second aspect, an abrasive member such as a grindstone or the like is prevented from being disengaged or cracked due to a sudden stoppage of rotation by continuously supplying a small amount of air from the air passage 23 so as to continue at low speed.
Further, in accordance with a third aspect of the present invention, there is provided an air tool with a safety device, wherein the rotary member 2 is directly connected to the output shaft 25 of the air motor 26, and the safety valve body 4 is supported to the rotary member 2 so as to be coaxial with a rotational axis thereof.
In accordance with the air tool with the safety device described in the third aspect, since the rotary member 2 and the safety valve body 4 are coaxial with the output shaft 25 of the air motor 26, the structure can be made more compact.
In accordance with a fourth aspect of the present invention, there is provided an air tool with a safety device, wherein the air tool with the safety device as recited in the third aspect further comprises: a speed adjusting valve body 7 arranged in such a manner as to slide substantially in a coaxial manner, third urging means 11 for urging the speed adjusting valve body 7 in a direction of moving apart from the valve seat 24, and a speed adjusting weight 12 supported to the rotary member 2 in such a manner as to be displaced due to a centrifugal force caused by the rotation of the rotary member 2, and wherein an interlocking mechanism for reducing the effective opening of the passage by moving the speed adjusting valve body 7 close to the valve seat 24 due to a displacement of the speed adjusting weight 12 is provided between the speed adjusting valve body 7 and the speed adjusting weight 12.
In accordance with the air tool with the safety device described in the fourth aspect, since the speed adjusting apparatus capable of automatically controlling the rotation rate in a coaxial manner with the safety device is mounted, it is possible to construct the safety device and the speed adjusting apparatus compact.
The invention provides an air tool with a safety device structured to automatically reduce a rotation rate and lock the air tool in a locked condition so as to inhibit normal use in the case that the rotation generated by an air motor of the air tool such as the air grinder or the like exceeds a predetermined rotation rate. The air tool with the safety device has a main body casing 22, an air passage 23 formed within the main body casing 22, an air motor 26 rotated by air supplied from the air passage 23, a valve seat 24 interposed in the air passage 23, a safety valve body 4 arranged in such a manner as to change an effective opening of the passage by moving in a direction of moving close to and apart from the valve seat 24, first urging means 6 for urging the safety valve body 4 in a direction of moving close to the valve seat 24, a rotary member 2 rotating in interlocking with an output shaft 25 of the air motor 26, a safety valve stopper 16 mounted to the rotary member 2 so as to be displaced outward in a diametrical direction due to a centrifugal force generated by a rotation of the rotary member 2 and second urging means 20 for urging the safety valve stopper 16 in a direction inverse to a direction in which the centrifugal force is applied. In this air tool with the safety device, a lock mechanism for locking a motion of the safety valve body 4 in a steady operation state that the safety valve body 4 moves apart from the valve seat 24 against an urging force of the first urging means 6 so as to increase an effective opening of the passage, disengaging the lock so as to move the safety valve body 4 in a direction of moving close to the valve seat 24 by the first urging means 6, thereby reducing the effective opening of the passage when a rotation rate of the output shaft 25 of the air motor 26 is increased to be over a predetermined rotation rate and the safety valve stopper 16 moves against the urging force of the second urging means 20 due to the centrifugal force, and again locking the motion of the safety valve body 4 in this state is provided between the safety valve body 4 and the safety valve stopper 16.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.